An aircraft gas turbine engine or jet engine draws in and compresses air with an axial flow compressor, mixes the compressed air with fuel, burns the mixture, and expels the combustion gases through an axial flow turbine to power a compressor. The compressor includes a disk with blades projecting from its periphery. The disk turns rapidly on a shaft, and the curved blades draw in and compress air.
In current manufacturing practice, the compressor is made by forging the compressor disk as a single piece with slots at the periphery. The compressor blades are individually cast or forged to shape with a root section termed a dovetail that fits into slots formed in the disk. Assembly is completed by sliding the dovetail sections of the blades into the slots in the disk. If a blade does not fit properly, fails, or is damaged during service, it may be readily replaced by reversing the assembly procedure to remove the blade, and providing a new blade.
Blades may also be formed integrally with the disk, in a combination termed a bladed disk or BLISK. This combination may also be known as an integrally bladed rotor. The BLISK approach to manufacturing offers the potential for increased performance through reduced weight. Such an article can be cast or forged as a large disk with an excess of metal at the periphery. The blades are then machined from the excess metal, integrally attached to the disk. The final product is expensive to produce, as it requires extensive high-precision machining operations. An error in machining even one of the blades may result in rejection and scrapping of the entire BLISK or an expensive and time consuming repair.
Replacement or repair of a damaged blade portion of the BLISK or turbine blade presents a difficult problem with this cast and machine or forge and machine approach. If all or a portion of a blade breaks off from impact of a foreign body during operation, for example, the BLISK becomes unbalanced. Damaged BLISKS may be repaired by welding excess metal into the damaged area and machining the metal to form the appropriate shape, or by cutting out the damaged area and replacing the cut out material by diffusion bonding a new piece into the damaged area. However, such an approach is both expensive and may result in reduced performance and durability.
A different approach to manufacture and repair BLISKS has been disclosed in U.S. Pat. No. 5,038,014, incorporated herein by reference. This approach utilizes a laser cladding or welding technique that feeds powders into molten material on the surface to be repaired, which produces a layer of new material. By repeating this process in a layer-by-layer fashion, these layers are built upon one another to form new parts or to repair damaged parts.
Past laser cladding techniques have resulted in imperfections and inclusions in the formed or repaired part resulting from lack of complete fusion between successive layers or extensive porosity of the deposited layers. These imperfections and inclusions are often associated with complex geometry of the formed or repaired part. Therefore, a need exists to provide a layered fabrication technique that solves the problems associated with the past manufacture and repair techniques.
Laser Net Shape Manufacturing (LNSM) provides an economical and highly flexible method to form and restore BLISKS, compressor blades and turbine components. The LNSM technique is based on laser cladding, wherein a laser is used to create a 3D geometry by precisely cladding thin layers of metal powder on a base material.
LSNM may be used in the fabrication of new parts and the repair of damaged parts. A Computer Aided Design (CAD) model of a part to be fabricated is uniformly sliced along the desired direction of material buildup. Powder is applied and fused along a tool path to create a material layer, layers are then built upon one another until the part is fabricated. Various tool paths have been used in applying the powders, the most common being a zigzag pattern or a stitch pattern, depending on whether the material is forming an internal area or a surface area of the part. However, prior LSNM methods result in inclusions of fusion imperfections and porosity in newly fabricated or repaired parts, requiring that the part either be scrapped or further processed to repair the imperfections. In addition, past laser deposition methods for fabrication and repair have not focused on producing accurate shapes and geometries.
Therefore, a need exists to develop an accurate LNSM method that reduces fusion imperfections and porosity that allows turbine components including BLISKS, compressor blades and turbine blades to be manufactured and repaired.